That about sums it up

“It’s a cultural ‘known’ that guys are into lesbian sex, but as you point out, they’re not REALLY into lesbian sex. What they’re into is having sex with two women who also….uh do stuff…to each other. A guy with two real lesbians would probably turn out like with Ross on friends: at first he watches all excited, then after 10 minutes he goes to make a sandwich! Real lesbian sex doesn’t include us fellas! That’s what makes it *lesbian*!”

–from the Whedonesque slash thread